1. Field of the Invention
The invention relates to a power control unit that controls a rotary electric machine that drives a vehicle, and that is mounted onto a motor case in which the rotary electric machine is housed.
2. Description of Related Art
Electric vehicles in which the vehicle is driven by driving force from a rotary electric machine such as a motor-generator, hybrid vehicles in which the vehicle is driven by a combination of a rotary electric machine and an engine that is an internal combustion engine, and fuel cell vehicles in which the vehicle is driven by electric power generated by a fuel cell, and the like are known. These kinds of vehicles are equipped with a PCU (power control unit) that receives a supply of electric power from a battery, and has a step up converter and an inverter and the like that control the electric power to a motor-generator (hereinafter, also referred to as “motor”).
Typically, in order to operate the motor efficiently, high voltage must be supplied. For example, a hybrid vehicle provided with a step up converter that steps up battery voltage of approximately 200 volts to approximately 600 volts is known. The step up converter includes a switching element and a reactor that is connected to the switching element. The reactor includes a core that uses magnetic material, such as an iron core, and a coil that is provided with the core. Also, the step up converter stores and releases electric power to and from the reactor by controlling the switching element on and off, thus enabling the voltage that is supplied from the battery to be stepped up and supplied to the inverter. At this time, in the reactor, the core generates heat from electromagnetic energy conversion, and the coil generates heat from the Joule heat of flowing current. If the heat is not suitably released, the temperature of the reactor will rise and the voltage conversion efficiency of the step up converter will decrease, so heat must be suitably released from the reactor. Thus, regarding heat release from a reactor, there is technology for releasing heat by cooling fins on the reactor, and technology for releasing heat using coolant, and the like.
Japanese Patent Application Publication No. 2008-72813 (JP-A-2008-72813) describes a drive apparatus of a hybrid vehicle that is provided with a step up converter of which a reactor is a constituent element. With the drive apparatus described in JP-A-2008-72813, in order to promote heat release from the reactor when the inverter and the motor are arranged together in a single case, lubricating oil that has been drawn up by the rotation of a motor-generator is made to flow into a housing chamber in which the reactor is housed, and the reactor is cooled by the lubricating oil stored in the housing chamber.
FIG. 5 is a view of a drive apparatus 100 according to related art, and shows a cross section of a motor-generator MG2 and a reactor L1 on the front side, and a differential gear, a power element substrate 109, a capacitor C2, and a cooler 108 having cooling vents 106 and 107 behind the motor-generator MG2 and the reactor L1. Lubricating oil is drawn up as shown by arrows F1 and F2, by the rotation of the motor-generator MG2, and lubricating oil that has passed through an open portion 340 in the housing chamber flows into a reactor housing chamber 300. The lubricating oil that flows in cools the reactor L1 and is discharged from an oil drain hole 320 to an open portion 102 as shown by arrow F3. This kind of structure makes it possible to ensure the cooling ability of the reactor L1.
As described above, with technology for cooling the reactor L1 using lubricating oil when motor-generators MG1 and MG2, a step up converter for driving these motors, and an inverter are all housed together, the temperature of the lubricating oil is regulated by coolant that cools a motor case and an engine case, so during normal operation, the coolant temperature and the oil temperature are substantially the same temperature (for example, approximately 85° C. to approximately 90° C.). On the other hand, in a heavy-load operating state, the heat rapidly generated by the engine and the motor-generators causes the oil temperature to become higher than the coolant temperature, so not only is the ability to cool the reactor a concern, but the transfer of heat to the step up converter and the inverter that are arranged near the reactor is also a concern.
The step up converter and the inverter and the like have power element substrates, and the temperature of these power element substrates is regulated by the temperature of the coolant in the cooler 108. Normally temperature regulation is performed by a large radiator and fan, but if heat exceeding the capacity of the cooler 108 is transferred to the cooler 108 in a heavy load state, the running performance of the vehicle may decrease due to output limiting control that accompanies a rise in the temperature of the power elements.
In particular, when the step up converter and the inverter that form the power control unit are arranged together with the motor in a single case as described above, the temperature of the power control unit will rise from heat conduction from the case, heat conduction from an aluminum die-cast cover that covers the power control unit, and the convective heat of the air inside the cover.